Many of various synthetic dyes discharged from the processes of staining fiber products and from dyestuff production processes are slightly biodegradable substances, involving much difficulty in the degradation thereof in the nature. Because such colored wastewater is hazardous for the nature, regulations over the wastewater have increasingly been tightened.
In the fields of staining industry and dyestuff production industry, wastewater containing dyes has conventionally been treated, mainly by physical or chemical methods such as adsorption, concentration, chemical transformation and incineration. Although these treatment methods are efficient, these methods disadvantageously involve secondary pollution due to the generation of hazardous byproducts and the discharge of the greenhouse effect gas via high-level energy consumption.
Recently, attention has been focused on a treatment method actively utilizing biotechnology with microorganisms or enzymes, as an alternative of the treatment methods. Several microbial strains capable of degrading dyes and colored substances have already been reported. For example, Phanerochaete chrysosporium as one species of white rot fungus is listed, which is known as one of lignin-degrading fungus.
However, all the dye-degrading microorganisms known so far have an activity to degrade only one or several types of dyes, so the ability of the microorganisms to treat dyes via degradation is naturally limited. Therefore, the development of an efficient method for treating of wastewater containing dyes has been desired.
Some of the present inventors have isolated a microorganism capable of degrading azo type- and anthraquinone type-dyes, namely Geotrichum candidum Dec 1 (which was internationally deposited at the National Institute of Bioscience and Human-Technology, the Ministry of International Trade and Industry, at 1-1-3, Higashi, Tsukuba, Ibaraki, Japan [transferred on Feb. 17, 2000 from the original deposit (FERM P-15348); the accession number was FERM BP-7033] from the nature and have developed a method for degrading and decolorizing a wider range of dyes by microbial treatment (Japanese Patent Laid-open No. 9-173051).
It has been assumed that the excellent ability of Geotrichum candidum Dec 1 strain to degrade dyes may possibly be based on the peroxidase activity of the fungal strain, but no instance of specific isolation or identification of such enzyme has been found. Hence, the genetic information thereof has absolutely never been elucidated.
The present invention has been attained toward the industrial demand as mentioned above. An object of the invention is to provide an enzyme applicable to more efficient treatment of wastewater containing dyes and a method for degrading and decolorizing dyes by using the enzyme.
The Geotrichum candidum Dec 1 strain exerts an activity to degrade a wide range of dyes and has also prominent enzyme stability. Therefore, the fungal strain per se or after immobilization on an appropriate carrier can be used for degrading dyes.
So as to enhance the industrial applicability, however, the treatment of wastewater containing dyes, particularly dye degradation should essentially be attained in an efficient manner economically.
It is useful for that purpose to use a dye-degrading enzyme owned by said microorganism through isolation and purification rather than to use the microorganism per se, to further elucidate the genetic constitution thereof to realize the mass production of the enzyme and to use them in combination.
The present inventors have made investigations so as to attain the purpose. Because the novel fungus Geotrichum candidum Dec 1 strain exerts wide decolorizing spectra over various dyes, the inventors have made further investigations with their attention focused on the dye-degrading enzymes produced by the fungus. The inventors have successfully isolated and identified one of the enzymes, elucidated the gene encoding the enzyme and developed a mass expression system of the enzyme.